This invention relates to an improvement in a polyvinyl chloride container for storing blood platelets.
There are a number of individuals whose blood is deficient in blood platelets and who therefore run the risk of serious complications should they require surgery or become injured since their blood will not clot properly. Such individuals require the intravenous administration of concentrates of blood platelets at the time of an injury or prior to surgery. Platelet concentrates are routinely obtained by well established procedures from blood plasma and are stored in medical grade polyvinyl chloride (PVC) bags either at around 4.degree. C. or at about 22.degree. C. prior to use.
Unfortunately the integrity of platelets is very short-lived when stored at 22.degree. C. and morphologic changes develop wherein the normal discoid platelets are transformed into spherical cells which are non-functional. These latter forms expire and are eliminated from the circulation. By labelling platelets with .sup.51 Cr, one can determine the degree of survival (% recovery) of viable cells at different periods following injection of platelet concentrates.
Platelet concentrates contain glucose (dextrose) as a consequence of the process by which they are collected since the blood has been collected in bags containing buffered anticoagulants such as ACD (acid citrate-dextrose) or CPD (citrate-phosphate-dextrose). During storage, the platelets convert glucose to lactic acid and carbon dioxide (CO.sub.2) which lower the pH. Murphy and Gardner (Blood, Vol. 46, No. 2, pp. 209-218, 1975) measured CO.sub.2 and oxygen pressures in various PVC and polyethylene (PE) bags containing platelet concentrates and observed that the drop in pH was greater the thicker the walls of the bag. Since oxygen is known to suppress conversion of glucose to lactic acid, it was concluded that the efficiency of oxygen transport into and CO.sub.2 transport from the bags was dependent upon the thickness of the bag walls. For a given platelet count, the pH drop of stored concentrates was significantly less for thin walled containers. Concentrates with high platelet counts (2.times.10.sup.6 /mm.sup.3 and greater) stored in standard PVC bags whose walls were considerably thicker had a pH of around 6.0 or lower after 3 days storage. Murphy and Gardner (Blood Vol. 35, pp. 549-557, 1970) have also shown that an abrupt loss of in vivo viability occurs if pH falls below 6.0 during storage.
Unfortunately, thicker-walled bags are necessary in the process of obtaining platelet concentrates since the bags are subjected to high speed centrifugation and must be resistant to rupturing. To achieve the degree of flexibility needed for standard PVC bags, the PVC contains a certain percentage of di-2-ethylhexyl phthalate (DEHP) plasticizer. Recently there has been increasing concern over the possibility of harmful effects derived from DEHP which leaches into biological products stored in standard PVC containers and which then is infused into patients. Although PE contains no plasticizers, it would not be a suitable material for bags in which to collect platelet concentrates any more than thin-walled PVC bags since they are highly susceptible to rupturing during pressure steam sterilization and/or centrifugation.
It would therefore be highly desirable to be able to store platelets in a plastic container having sufficient tensile strength to withstand pressure sterilization and high-speed configuration while at the same time having good carbon dioxide and oxygen permeability characteristics so as to prolong platelet survival. It would be a particular advantage if platelet survival could be prolonged beyond the usual three day survival period. Currently, blood banks must discard platelets after three days storage which makes it difficult and expensive to maintain supplies for emergency situations.